Rheostat



June 9, 1936. 'N. c. SCHEILLENGER 2,043,777

RHEOSTAT Filed May 26, 1935 4 sheets-sheet 1 Inventor.-

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June 9, 1936. N. c. SCHELLENGER RHEOSTAT Filed May 26, 1955 4 Sheets-Sheet 2 I mz/enwr; Newton C5572 eZZe mm? 4;

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June 9, 1936.

N. C. SCHELLENGER RHEOSTAT Filed May 26, 1933 4 Sheets-Sheet 5 INSULATION 1727;572:07 [Yea/$072.6 55/26 Z Zenyen 5 v June 9, 1936. N. c. SCHELLENGER RHEOSTAT Filed May 26, 1935 4 Sheets-Sheet 4 [Yea/23022 I'm/enter.- 6, Sc/zeZZefi er 7% Patented June 9, 1936' PATENT OFFICE RHEO STAT Newton 0. Schellenger, Elkhart, Ind., assignor to Chicago Telephone Supply Company, a corporation of Indiana Application May 26, 1933, Serial No. 672,955

12 Claims. (01. 201-55) My invention relates to an electrical circuit control device and relates more particularly to a rheostat as commonly used in radio circuits.

In my copending application, filed December 7-,

s 1931, Serial No. 579,552, issued as Patent No.

1,920,217, Aug. 1, 1933, and of which this is a continuation in part, I have shown a variable resist ance unit or rheostat, commonly known as a volume control, combined with a switch; both the 10 switch and rheostat being actuated from the same operating shaft.

- It is an object of my invention to employ a spring arm of very light material, which engages the contact shoe of the resistance element.

15 w A further object of my invention is to embody an inconspicuous, serviceable device whereby a violent jolt of the unit will not dislodge the contact shoe from the pressure arm.

A further object of my invention is to construct the terminal members so that an inadvertent bending or displacement of the low resistance terminal member will cause no change in the low resistance hop-off.

Otherobjects of this invention are to provide an improved device of the character. described, that is easily and economically produced, which is sturdy in construction and which has a maximum of efficiency and accuracy.

With the above and related objects in view, my invention consists in the following details of construction and combination of parts,- as will be more fully understood from the following specification, taken in conjunction with the drawings, in which:- 7

Figure 1 shows a fragmentary sectional view of my'invention embodied in a rheostat and combined with a snap switch;

Figure 2 is a plan view ofthe resistance element 1 and terminals;

Figure 3 is a perspective view of the contactor arm, its support and shaft; I

Figure 4 is a rear view of the contactor arm support, showing the unsynnnetrical placing of the holding rivets; Figure 5 is a fragmentary side elevational view showing the swedging out of the shaft holding as bakelite.

Figure 9 is a fragmentary side elevational view I showing the attachment of a terminal;

Figure 10 1s a fragmentary plan view of the terminal;

Figure 11 is a plan view of a modified contactor arm and-contacting shoe;

Figure 12 is a front view of the shoe and contacto-r arm shown in Figure 11;

Figure 13 is a fragmentary sectional view of a tandem arranged rheostat embodying my invention;

Figure 14 is a plan view of another type of pressure arm wherein the arms are supported in a in Fig. 1.

Figure 21 is a plan view of my rheostat, showing a cover grounding plate and positioning lugs.

Figure 22 is a broken sectional view of the rheostat shown in Figure 1.

Referring nowto the drawings in more detail,

particularly to Figs. 1, 2 and 3, it will be seen that the instrumentalities of the rheostat are mounted upon a base or mounting disc In which may conveniently be formed of an insulating material such as phenol condensation product commonly known The resistance element l2, preferably a carbonaceous coated strip or generally arcuate shape, is placed upon one of the flat faces of the base or mounting disc Ill, and is held thereagainst by terminal members ll and 16 engaging its ends.

As will be seen in Figs. 2, 9 and 10, the terminal member l6,.of a single strip of conducting material of uniform thickness, has a foot l8 disposed in engagement with one end of the resistance element l2 and is pierced for the reception of an attaching means, shown for convenience as an eyelet 20. The foot portion I8 of the terminal contains an arcuate recess 22 so that the length of the terminal edge in close proximity to the shoe, when the shoe is adjacent the terminal, will be greater than if the terminal had a straight edge extending across the resistance element, and, as a consequence the minimum resistance between shown in the terminal l4 of Fig. 2, to engage an edge of the resistance element to provide for a slow resistance increase upon the arcuate'movement of a contact shoe 28. In this manner, virtually any desired initial resistance gradient may be obtained.

A similar arrangement may be embodied at the high resistance terminal, and the only thing necessary will be to make the high resistance terminal complementary to the low resistance ter-. minal, that is, one of the members is a right hand member and the other a left hand member.

The diverging extension 24 also functions to keep a low initial resistance in the circuit until the switch, mounted on the cover, is closed.

' The neck 30 of the terminal I6 is bent sharply adjacent the foot portion l8 and is fitted in a slot 32 in the periphery of the mounting plate ill to prevent the terminal member from being turned circumferentially with respect to this plate. The neck is then turned back upon itself and tapers in width, as indicated at 34. The terminal extends at an-an'gle to the plane of the cylindrical casing face'to permit the easy attachment ofthe various lead wires. To prevent the displacement of the foot portionof the terminals [4 and IS with a consequent increase in the minimum resistance, should there be an axial bending of the terminals, narrow sections i5 and I! respectively have been provided in the lug portion of the terminals so that bending will first take place at these points and no'harm result.

Bushing Mounted concentrically in the disc I0 is a suitable journal bushing or thimble, generally designated as A, which may also serve as a panel mounting device for the unit. This bushing A may be threaded exteriorly as at 36 for the reception of a nut by which the assembly is clamped upon a suitable panel or bracket, that is, by the usual and well known type of mounting, and the bushing also has a central longitudinal opening 38 therethrough.

. The bushing A contains an annular flange 40 disposed against the surface of the disc l0 upon which the resistance element I2 is located, and if desired, this flange 40 may be serrated on one face as shown at 42 so that it will bite into the disc Ill and lock that disc against rotation with respect to the bushing.

7 A shoulder or swaging portion43, of smaller diameter than the flange and emerging from the flange, protrudes through the base opening 44 and also through a central opening. in a holding clamp B, and the end of the shoulder 43 is swelled to grip the face of the clamp and to engage a plurality of spaced niches 46 (Fig. 20) in the clamp B for the prevention of rotary motion of the disc and the holding clamp B in a direction about the axis of the shaft, and in a direction along the shaft. If further rotational restraint is desired, burrs are'provided along the radial rheostat is to be mounted, and prevent rotation of the rheostat relative to the panel.

contactor arm stantially of circular formation, has a plurality.

of extending cars 52 and 54 on the periphery adapted to engage a suitable stop member 56 pro truding from the stud 4 for limiting the rotation of the arm in either direction, and the plate, also, has a central elongated opening 58 to fit onto the end 50 of the shaft. The insulating plate is placed upon the reduced end 50 of the shaft 48 and a washer, generally designated E, having a central opening to also fit onto the reduced end 50 of the shaft is placed thereon and the face of the reduced end is then swaged over, holding the shaft C, the plate D and the washer E in position, The washer has, see Figs. 7 and 8, a plurality of radial slots or notches and 62 with burrs BI, 63, 64 and 65 along the radial edges of the notches, which burrs are adapted to bite into the insulating plate,'thus preventing relative rotation of the shaft and insulating plate.

A resilient contactor or pressure arm F, preferably of a 'sihgle piece of suitable thin conducting material and supported by the plate D, is

- comprised of an arcuate shaped cantilever arm 66 supported at each'e'nd by integral formed yoke portions 68 and 10, which yoke portions in turn are united to a 'central slip-ring section 12 having an internal diameter substantially larger than the diameter of the shaft 48, as shown in Figure 3, to space the slip ring section from the shaft in an insulating relationship thereto. The contactor arm is also provided with a peripheral cutout portion 14,- which is adapted to fit about an eccentrically mounted operating pin 16 carried by the insulating plate D. The arcuate shaped arm has verging from its unsupported mid-portion a projecting tip or boss 18 adapted to engage the perforated disc or shoe 28, which engages the resistance element. However, the tip may be constructed to actually engage the resistance element, or may take a variety of forms as shown in Figs. 11 and 12, as hereinafter more fully described.

A modified pressure arm G, Figs. 11 and 12, has a short conical boss 80 and two projecting lugs 82 and 84.

A fiat contact shoe 85 has two diametrically opposed holes 86 and 88 therein, which receive the projecting lugs 82 and 84, respectively, of the pressure arm. The pressure exerted by the arm G is directed against the central portion of the shoe 85 by the conical boss'80 engaging the upper surface of the contact shoe.

The contact shoe is drawn along the resistance element by one or the other lug of the pressure arm engaging the edge of one of the holes in the shoe 85, so that the shoe is always pulled along ,the resistance element.

The contactor or pressure arm F is mounted upon the insulating plate by means of suitable edges .of the niches 46, so that they engage the eyelets or'rivets 90 and.92, see Figs. 3, l6 and 17,

disc 10 when the shoulder 43 of bushing A is' swaged in place. This very definitely locks the disc l0 and clamp B together and may be used instead of the knurling 42 on the flange 40. Pro- 'truding lugs 39 on the clamp B are adapted to cooperate with holes in the panel, upon which the which eyelets or rivets are unsymmetrically placed, as will be hereinafter further described. The arm F is so mounted that the tip 18 will be approximately equi-spaced from the extending ears 52 and 54, Fig. 17.

Now referring again to my preferred embodi- 75 Pressed out projections 96 and 98 to each side of the free end of the cantilever arm and extending in a direction opposite to that of the tip I8 are adapted to engage one face of the insulating disc to prevent the contacting shoe from separating from the lug I8.

Considerable diificulty is experienced when manufacturing rheostats, in securing a uniform predetermined pressure between the contacting shoe and the resistance element, and between the spring member K and the contact arm F, both ofwhich are very necessary if low resistance contacts and long life are to beexpected. Predetermined pressures are obtained with my rheostat by assembling the parts in proper axial alignment and then applying the desired pressure to the shaft 0 in an axial direction and in such a manner that it is resisted by the pressure between the contacting shoe and resistance element plus the pressure between the arm F and spring member K. These pressures are maintained by swaging the shaft, when in the desired position (Figs. 1,,5-and 6), at IOI,so that it is enlarged at this point and forms a shoulder that bears against the washer I00, which is in contact with one end of the thimble A.

It is particularly to be noted that with this method of assembly, no unnecessary strain what-v soever is placed upon the cont-actor or resilient arm by pressing the contact shoe 28 in engagement with the resistance element during the swaging action.

Slip-ring and washer Disposed upon the surface I02 of the thimble A isan insulating washer J, Figs. 1 and 2, having dPametrically placed peripheral notches I04 and I06 therein.

'A ring-shaped slip-ring member, generally designated K, and having a concave face I08 adjacent the insulating washer J, has a short lug I I0 and a long lug I I2, Figs. 1, 2 and 13, extending from the periphery of the face I08. The lugs H0 and 2, when suitably bent, extend or fit into the notches I04 and I06 of the insulating washer, and the long lug is also adapted to provide the electrical take-off for the derived electrical circuit. The stud II4 serves to connect the long lug II2 of the slip-ring member to a terminal H5 and secures the slip-ring and terminal in electrical'relationship. It is to be particularly noted, see Fig. 1, that the slip-ring K is .axially resilient to provide a good electrical contact with the movable slip-ring I2.

Both the washer J and the slip-ring member.

K are provided with central, aligned openings for receiving the control or operating shaft C, the apertures formed in the slip-ring member K being of a larger diameter than the opening or aperture through the washer J, so the slip-ring member K will be spaced from the-control shaft and thus insulated therefrom.

Tandem Heretofore, the tandem or double type of rheostat construction, in which the pressure arms were insulated from each other (shown in Fig.

'13), required a large casing, but by my novel unsymmetrically arranged contact arm F sup-- 16 and 17) by eyelets 90 and 92, I economize in space by placing an additional contact arm H, similar in structure to the arm E, (but one arm being so-called right-handed and the other left-handed) upon the vacant face II8 of the insulating strip and securing it in place with eyelets 9i and 93. It will be noted that there is no electrical connection between the two arms, as each arm is cut out both to clear theeyeiets that hold the arm in place, and .to clear the shaft. I have thus provided an insulated pressure arm for the second rheostat section without the addition of another shaft, bushing, or mounting plate,

such as has been used in the past. The second rheostat section is comprised of a second insulating base I20, held in the housing I40 by the eyelet MI, and positioned angularly by formed in sections in the housing co-operating with notches in the periphery of the base I20. A resistance element I43 is'carried by the base I20 and is contacted by a shoe I44 driven by the pressure arm Ha Terminals for the resistance element and for the spring connector K, which contacts the arm H, are provided and extend through notches in the base I20 and through an opening in the metal housing I40 that is sufllciently large to provide good insulation.

Switch operation In order to provide for the operation of a a switch or circuit controller, the insulating disc D may be provided with an eccentrically mounted pin 16.

This pin I6 projects normal to the plane of the insulating disc and is located to engage an 1 The casing II, within which the rheostat is housed, is provided with a plurality of projecting ears I50, which are registered in peripheral slots I24, I26, I28 and I30 on the base and bent over to attach the casing to the plate. The registration of the ears with their respective slots I24, I26, I20 and I30, accurately aligns and holds the housing with respect to the plate both in a rotary direction about the axis of the shaft and in a direction along the shaft. By this means, the alignment of the rheostat and switch may be predetermined so that the two will function cooperatively.

The casing or housing for the rheostat, which also supports the switch, may be attached to the base by any suitable means, but preferably by the means as disclosed in either of my copending applications, Serial No. 668,757, filed May 1, 1933 or Serial No. 671,031, filed May 15, 1933.

It is in many cases advantageous to provide a rheostat enclosed almost entirely in metal; so

that all of the operating parts are electrostatically shielded from outside electrical disturbances. This is especiallytrue when a switch is switching a fluctuating current.

I have found ported upon the insulating baseD (shown in Figs. it possible to very efliciently and economically accomplish both of the above results with the plate L (Figs. 21 and 22) from which the lugs 239 are formed. Plate L is mounted over the base it) so that the insulating base is almost completely shielded. This plate L is also in electrical contact with the mounting bushing or thimble A, which will normally be mounted on a grounded metal panel, and has clinched over onto it the ears I50 of the cover member II. It is therefore necessary to ground only the thimble to accomplish the necessary electrostatic shielding of the rheostht from the switch and other external disturbances. In many instances, it is possible to efiect economies in the manufacture of radio sets by extending the grounding plate to one of the terminals of the resistance element.

In Fig. 21, I have shown plate L carrying a terminal ll, w ich replaces one of the regular terminals. This terminal is normally connected to ground by virtue of being a part of the plate L, which is normally grounded. It is also con.- nected to one end of the resistance-element (the end that isdesired to be grounded) by the eyelet 2M and a washer or plate on the inside of the rheostat bearing against the element and held in place by the eyelet. When a grounded terminal is not desired, the plate L is made according to the dotted lines 210.

Two ears 239 integral with the plateL and formed at right angles to it are adapted to register with holes in the mounting panel to prevent rotation of the control relative to the panel during assembly and afterward. A washer or spacer 216 is assembledon the thimble A, preferably in a permanent manner, to provide an even substantial mounting surface and to space the terminals and ears away from the panel Referring now to Figs. 14 and 18,1 show a pressure arm of the same general type as, but having certain valuable improvements over, the arm covered in my Patent No. 1,913,686 of June 13, 1933. With the arm of my prior patent there was a tendency for the two converging sections to twist when a pressure was applied against the contact paddle, due to the bowing of the yoke section caused by the pressure on the endsfof the yokebeing in a reverse direction to that on the contact projection. This twisting seriously impaired the flexibility of the arm as, a whole, since the legs were freeto bend in the desired direction for only a small; part of their total length, the balance of their length being twisted andnot free to bend.

This is overcome in the arm disclosed in Figs.

14 and 18 bystrengthening the yoke carrying the lug M2 by a rib or offset portion 2H1, and by strengthening the rear section with a rib or offset portion 2. By strengthening the front and rear yoke portions in this manner, twisting of sections 204 and 206 is prevented, and.a good distribution of flexing obtained.

1 have'accomplished this same end in the arm shown in Figs. 15 and 19 by securing the ends of portions 250 and 252 to the plate 254, which is quite rigid, by eyelets 256 and by strengthening the front yoke portion by bending a portion 262 at a substantial angle to the main (part of the yoke 258.

Although the invention has been described in considerable detail, such description is intended as illustrative rather than limiting, as the invention may be variously embodied, and the scope of the invention is to be determined asclaimed.

I claim as my invention:

c 1. A variable resistance device comprising, a mounting thimble, a serrated enlarged head on said thimble, a shoulder of lesser diameter and emerging from said head, an insulating base having the serrations engaging one face of said base, a mounting washer having an irregular opening therein and engaging the opposite face of said base, said shoulder of the thimble being expanded to hold the thimble, base and mounting washer together.

2. A tandem unit variable resistance device comprising a pair of spaced opposed bases, a resistance element on each of said bases, a rotatable shaft extending through at least one of said bases, an insulating plate carried by said shaft between said bases, contact arms mounted respectively on each side of said plate, contact shoes engaged by said contact arms respectively and bearing against the corresponding resistance elements, and oppositely disposed resilient means arranged on each side of said plate and bearing on each of said conta tzits1 arms to establish electrical connection there- Wi 3. A tandem unit variable resistance device comprising a housing having a pair of spaced'substantially parallel end walls, a flat resistance element on the inside face of each of said end walls,

a rotatable shaft extending through at least one of said end walls, a flat plate carried on said shaft and dispo:ed between and substantially parallel to said end walls, a resilient contact arm on each side of said plate respectively, means securing said arms respectively to said plate at an end of each arm, a contact shoe bearing upon each resistance element respectively and engaged respectively by 'the free ends of said resilient arms, and a pair of spring tensioned collector brushesfeach disposed on opposite sides of said plate in electrical engagement with each of said contact arms, respectively, said brushes being disposed to exert axial thrusts on said shaft through said plata'the ,wals, a flat insulating'plate disposed between said end walls and carried on said shaft, a,resilient contact arm on each side of said plate respectively, means securing an end of each contact arm respectively to said plate, a contact shoe bearing against each of said resistance elements respectively and engaged by the free ends of the corresponding contact arm and a resilient current collecting member interposed respectively between said plate and said end walls respectively to resiliently position said plate in said housing.

5. A variable resistance device comprising a base, a resistance element on said base, a terminal h ving an arcuat'ely recessed portion overlying and contacting the surface of said resistance element, a disk-like contactor engaging and movable over the surface of said resistance element and shaped to nest in the recessed portion of said terminal, and ineans engaging said contactor for moving the same over said resistance element and into the recess in said terminal wherein said shoe lies substantially concentrically when nested in said recess.

6. The combination with a switch, of a variable resistance device comprising a housing carrying 8810. switch, a resistance element in said housing,

- a terminal engaging said resistance element adrninal having an arm extending along a margin of that portion of the resistance element traversed by the contactor during that portion of its travel wherein said switch is operated.

7. The combination with a switch, of a variable resistance device comprising a housing carrying said switch, a resistance element in said housing, a contactor movable over the surface of said resistance element, a terminal engaging said resistance element adjacent one end and having an elongated leg extending in the direction of and adjacent the pathof said contactor, means including an arm for moving said contactor, and means including an element carried by said arm for actuating said switch during the movementof said contactor along that portion of its path adjacent said elongated leg.

8. In a variable resistor, a base member, a shaft journalled in said base member, a contactor secured to said shaft for movement therewith, a slip ring carried by said contactor, a spring collector ring spaced from and concentric with said shaft disposed between said contactor and base member, said collector ring being tensioned to exert an axial thrust on said shaft through said contactor, and an elongated appendage extending from said collector ring adapted to connect said contactor to an outside circuit.

9. In a variable resistor, a housing, a threaded mounting thimble centrally disposed in one wall of said housing, a shaft journalled in said thimble, a contactor secured to said shaft for movement therewith, a spring collector ring positioned upon said thimble in engagement with said contactor, a

tail member extending from said collector ring, said tail member being fastened to maintain said collector ring in spaced, concentric relation to said shaft, and an insulative member interposed between said thimble and said collector ring.

10. In a variable resistor, a base member, a bushing carried by said base member, a shaft journalled in said bushing, a contactor mounted on said shaft for rotation therewith, an insulative disc disposed to overlie said bushing, a resilient metal brush disposed about said shaft tensioned between said contactor and said insulative disc and having a bearing on each of them.

11. In a variable resistor, a base member, a

'bushing carried by said base member, a shaft bushing, a contactor mounted on said shaft for 0 rotation therewith, an insulative disc disposed upon said bushing, a resilient metal brush compressed between said contactor and said insulative disc, a conductive tail extending from said brush, said tail being secured to said base for making connection to an outside circuit, and positioning means for said brush comprising portions on said disc, brush and tail cooperating to fixedly mount said brush relative to said base spaced from contact Withthe shaft.

NEWTON C. SCHELLENGER. 

